A present water pump which is quickly mounted and demounted is usually provided with a filter which is convenient to dismount so as to clean debris on the filter and prevent the debris from blocking a water inlet. However, a user will often forget to mount the filter while using the water pump, making the water pump operate without a filter; in this way, the sundries in the sewage and big particles are easily sucked into an impeller cavity of the water pump when the water pump is operating to damage the impeller and reduce the service life of the water pump.